Microcapsules have been used for various applications. Recently, microcapsules have been used for smart coatings for corrosion applications. For instance, the pH-sensitive microcapsules disclosed by Li and Calle in 2009 NACE International conference paper 09499, 2007 NACE International conference paper 07228, and in U.S. Pat. No. 7,790,225 B1 (Luz Calle et al., issued Sep. 7, 2010) have been used for the controlled release of a corrosion indicator, or a corrosion inhibitor, or a self-healing agent when corrosion occurs. Mechanically breakable microcapsules are also used in self-healing composites disclosed by White, et al. in Nature, 2001, 409:794-797.
Existing microcapsules are typically formed from an oil-in-water or water-in-oil emulsion and have a wall encapsulating an interior core with an active agent. The active agent is released when the microcapsule wall breaks down mechanically or chemically.